As of June 2013 the Jena developers agreed to treat SDB as
being only maintained where possible.
See Future of SDB thread on the mailing list.

The developers intend to continue releasing SDB alongside other Jena
components but it is not actively developed. None of the developers
use it within their organizations.

SDB may be revived as a fully supported component if members of the
community come forward to develop it. The Jena team strongly recommends
the use of TDB instead of SDB for all new development due to
TDBs substantially better performance and scalability.